1. In alpha decay, the In beta decay, a neutron In gamma decay
nucleus loses 2 changes to a proton and there is no change Isotopes = have the same number of protons but
Gaining an electron = atom different number of neutrons eg C-12 and C-14 are
protons and 2 an electron, which gets in the atomic or
becomes a negative ion isotopes of carbon
neutrons, so the ejected, so the atomic mass number – only
Losing an electron = atom Atomic number = number of protons. eg for Helium, it is 2
atomic number goes number goes up by 1, energy is emitted.
becomes a positive ion Mass number = number of protons and neutrons. eg for
down by 2, while the while the mass number
mass number goes is unchanged. eg C-14 Helium, it is 4
down by 4. decays to N-14
GAMMA – stopped
ALPHA – stopped by
Properties The neutron has roughly the same
by lead. mass as a proton, but no charge. An
paper BETA – stopped by a
electron is very light, about 2000
thin sheet of aluminium
times lighter than the proton.
Smoke detectors: the source emits alphas, which
produce ions. The smoke stops the alphas.
Radioactive decay Thickness gauging: of paper or plastic using beta
particles.
Uses Radiotherapy: gamma source kills cancer cells.
Tracers: in the body or in underground pipelines
The Nucleus Carbon dating: C-12 is stable but the C-14 is
radioactive and we know its half-life.
Measure the ratio of the activities.
Half life Finding the age of rocks: measure the ratio of
uranium to lead.
Energy from
the nucleus
The radioactivity, in counts per minute, will In fission, a nucleus of uranium 235 or
decrease with time. Every half-life the count Plutonium 239 absorbs a neutron, and
decreases by a half. For example, Carbon 14 has splits.
a half-life of 5700 years. So after 3 half-lives Origins of background It gives out a lot of energy, and two or
(17, 100 years) the radioactivity has decreased radioactivity three further neutrons.
by a factor of 1/8 A chain reaction can occur if those
neutrons go on and split more nuclei.
Control rods in a reactor capture
Radon, coming from uranium in the ground. neutrons.
Cosmic rays, particles from outer space.
Rocks and the ground.
In fusion, two hydrogen protons join at
very high temperatures to form
helium. Happens in stars.